Rotating Around the y-axis (Frustums)
In the sketch below, you can drag the slider to change the parabola.
The area under the parabola is broken up into 1-unit wide trapezoids.
If you rotate each trapezoid around the y-axis, you create a bundt-cake-like solid.
The surface area is STILL approximated by the LSA of a frustum.
The list of numbers at the bottom of the graph shows the LSA of each frustum (from left to right).
The actual surface area is show next to the parabola equation.
Try a couple for practice!